Rotatable drying drum

ABSTRACT

A rotatable drying drum is provided with a drum wall having insertions and a combustion means for natural or liquid gas so that stone minerals can be dried and heated for the preparation of bituminous building materials. The combustion means includes a plurality of individual burners which are located in an end region of the drying drum.

United States Patent [191 Heise [111 3,840,337 [451 Oct. 8, 1974 3,132,023 5/1964 Backstroni 432/112 ROTATABLE DRYING DRUM [76] Inventor: Carl-Hermann Heise,

gzg gn 3220 Alfeld Primary Examiner-John J. Camby y Attorney, Agent, or Firm-Roland I. Griffin [22] Filed: June 7, I973 [21] Appl. No.: 368,043

' [57] ABSTRACT [30] Foreign Application Priority Data June 8, 1972 Germany 2227792 A rotatable drying drum is provided with a drum wall having insertions and a combustion means for natural [52] US. Cl. 432/105, 432/111 or liquid gas so that stone minerals can be dried and [51] Int. Cl. F27b 7/10, F27b 7/14 heated for the preparation of bituminous building ma- [58] Field of Search 432/103, 105, 112, 119, terials. The combustion means includes a pluralityvof 432/111 individual burners which are located in an end region of the drying drum. a [56] 7 References Cited UNITED STATES PATENTS 10 Claims, 2 Drawing Figures 3,031,176 4/1962 Ankersen 432/119 L-l c L-I (J l CDL'JOEIOEIOE] J' E! O D O E] O E! o 3 [1:1 1:] 1:! O III O E] O El O E] O PATENTED'um 8 m I 3840.337

SHEEI 1 of 2 CIQEIOUOEIO OEJOEIOEIOE] UOEIOUQEIOIII I OEIODQEICDEIC) DODOXGODQU j o o orfiom ROTATABLE DRYING DRUM BACKGROUND OF THE INVENTION This invention is related to a rotatable drying drum for drying and heating stone materials for the preparation of bituminous building materials. The drying drum has a drum wall that is provided with insertions and has a combustion means for natural or liquid gas. Such drying drums are well-known. They serve to dry and to heat stone minerals of the different grain sizes. During the manufacturing process of bituminous building ma terials, bitumen and other materials are added to the heated stone minerals.

Drying drums of this kind are operated in the onedirection mode as well as in the counter-current mode. At one end of the drum, centrally in its front wall, there is located a burner that is directed into the interior of the drum and that, for example, can be heated with oil or gas. The central supply of the energy medium, oil or.

gas, requires a relatively high temperature for the firing space in the region of the firing and burning-out area. Displacement of the burning-out area, may lead to an incomplete combustion. When oil is used as a fuel, there is the danger of a carbon deposit and of an oilmist deposit on the drying material. When gas is used, there is the danger of an incomplete combustion of the gas/air mixture with subsequent puff-effects in the exhaust pipes.

During the drying and heating process of stone minerals of the different grain classifications, the following problems are encountered. The power requirements of present day equipment exceed several hundreds of tons per hour. The use of hot bitumen and the preparation of melted asphalt require final temperatures greater than 180C. For this purpose the heat requirements are already in the range of 25,000 kw/hr. The exhaust'gas quantities of more than [00,000 m should be purified to an extent of less than 150 mg/m because of the safety conditions for protecting the environment. Be-

cause of environment protection, the use of fuel oil is an angle of about 45 with respect to a tangent to the cylindrical wall of the drying drum. Insertions comprising relatively small boxes are provided between the burners, while that part of the cylindrical wall of the drying drum not occupied by burners has insertions comprising relatively large boxes. The individualburners have separate outlet cross sections for the gas and the combustion air.

The inventive rotating drying drum has several advantages over the prior art. By dividing the combustion means into a plurality of individual burners a better control of the combustion process is possible. For example, it is possible to combust without excessive air,

only possible under special safety conditions in order to prevent the oil from penetrating the ground. Furthermore, the exhaust gases should not contain sulphurous or phosphorous compounds.

SUMMARY OF THE INVENTION It is the principal object of this invention to overcome the shortcomings of the prior art and to improve a drying drum of the initially described kind such that a better solution to the aforementioned complex problems is given. It is especially of importance to assure a good combustion of the combustion gases. Furthermore, the drying drum s'hould be usable for the different grain classifications.

According to the invention, this object is achieved by providing a rotatable drying drum with combustion means composed of a plurality of individual burners that are'located in a final region of the drying drum. The individual burners of the combustion means are located in the region of the front wall and the adjacent cylindrical wall of the drying drum. According to a preferred embodiment, about half the length of the cylindrical wall of the drying drum is occupied by individual burners. In the region of the cylindrical wall of the drying drum, each of the individual burners is inclined against the direction of rotation of the drying drum at while the preparation of the gas/air mixture can be accomplished substantially more accurately than with the prior art. Furthermore, a large surface of flames is pro vided in order to achieve a good heat transfer. Thus, relatively cool exhaust gases can be taken from the drying drum and can be supplied directly to a filtering means. By distributing the burners along a part of the cylindrical wall of the drying drum a rather extensive heat exchange is made possible because of .the direct contact. Adaptation of the individual burners to the various grain size classifications does not cause any difficulties, as power changes in the combustion can be controlled simply. In the region of the burners, the insertions comprise relatively small boxes in order to transfer as much as possible of the heat by contact. In

the part of the drum that is not occupied by burners, the heat has to be transferred substantially by convection. This is achieved by using insertions that comprise relatively large lifting boxes and therefore effect an intensive movement of the materials to be heated. The stone minerals are picked up by the boxes and are moved in a free fall. Thus, convective heat is transferred by the heating ga s to the stone minerals. The permanently free-burning burners in the upper region of the drying drum prevent an expiration of ignition of v the ignitable gas/air mixture in the part of the drum that is covered by stone minerals since the free-burning burners permanently act as ignition burners. By the simple control of the pressure of the gas and combus- I tion air it ispo ssible to optimize the drying effect during the drying process of the homogeneous individual grain sizes.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1 and 2, the drying drum is constructed in a usual manner. It has a cylindrical side wall 1 with end regions'which pass over into back and front walls 2 and 3. The drying drum is located in a substantially horizontal or slightly inclined-position. It is rotatable and has a usual drive means. A material inlet is provided in the back wall 2 as indicated by the arrow 4, and a material outlet for the dried andheated stone as indicated by invention, a plurality of individual burners 6 are provided in the region of the material outlet when the drying drum is operated in the countercurrent mode. Preferably, the individual burners 6 are distributed over the front wall 3 and over about half of the length of the cylindrical wall 1 of the drying drum. Between the burners 6 are insertions 7 comprising relatively small lifting boxes. In the remaining part of the drum, which is not 1 will be opposite from that indicated in the drawing.

It is essential that the combustion means be subdivided into a plurality of individual burners in order to,

obtain a better control of the gas/air mixture and to improve the mixing and combustion results. For example, a combustion without excessive air is made possible. This results in the maximum temperature that can be a second side portion thereof adjoining the other off said end portions, and a plurality of individual burners? mounted within said drying drum along said second side portion thereof with said smaller material lifting. members and along said other end portion.

2. Apparatus as in claim 1 wherein said second side portion of said drying drum extends over about half the;

length of said drying drum.

3. Apparatus as inclaim 1 wherein said burners are' inclined against the direction of rotation of said drying drum at an angle of about 45 with respect to a tangent to said drying drum. i

4. Apparatus as in claim 1 wherein said burners have separate outlet cross sections for a combustion gas and for air. F

5. Apparatus as in claim 1 wherein said material lifting members comprise material lifting boxes. 3

6. Apparatus as in claim 1 wherein said drying drum includes a cylindrical sidewall and a pair of end walls adjoining opposite ends of said cylindrical sidewall, said pair of material transfer ports is positioned in said end walls, said first plurality of material lifting members obtained with the combustion. A good control capability of the combustion means allows the specific treatment of each grain size. In summary, the heat transfer is substantially improved such that exhaust gases can also be purified without repeated cooling. I claim: I i

1. Apparatus for drying and heating stoneminerals for the preparation of bituminous building materials, said apparatus comprising a rotatable drying drum, a pair of material transfer ports positioned in a pair'of opposite end portions of said drying drum, a first plurality of material lifting members mountedwithin said drying drum-along a first side portion thereof adjoining one of said end portions, a second plurality of smaller material lifting members mounted within said drying drum along is mounted along a first portion of said cylindrical sidewall adjoining one of said end walls, said second plurality of smaller material lifting members is mounted along a second portion of said cylindrical sidewall adjoining the other of said end wallsfand said plurality of individual burners is mounted along said second portion of said cylindrical sidewall and said other end wall.

7. Apparatus as in claim 6 wherein said'second portion of said cylindrical sidewall extendsover about half the length of said drying drum.

8. Apparatus as in claim 7 wherein said burners are inclined against the direction of rotation of said drying drum at an angle of about 45 withrespect to a tangent to said cylindrical sidewall. 

1. Apparatus for drying and heating stone minerals for the preparation of bituminous building materials, said apparatus comprising a rotatable drying drum, a pair of material transfer ports positioned in a pair of opposite end portions of said drying drum, a first plurality of material lifting members mounted within said drying drum along a first side portion thereof adjoining one of said end portions, a second plurality of smaller material lifting members mounted within said drying drum along a second side portion thereof adjoining the other of said end portions, and a plurality of individual burners mounted within said drying drum along said second side portion thereof with said smaller material lifting members and along said other end portion.
 2. Apparatus as in claim 1 wherein said second side portion of said drying drum extends over about half the length of said drying drum.
 3. Apparatus as in claim 1 wherein said burners are inclined against the direction of rotation of said drying drum at an angle of about 45* with respect to a tangent to said drying drum.
 4. Apparatus as in claim 1 wherein said burners have separate outlet cross-sections for a combustion gas and for air.
 5. Apparatus as in claim 1 wherein said material lifting members comprise material lifting boxes.
 6. Apparatus as in claim 1 wherein said drying drum includes a cylindrical sidewall and a pair of end walls adjoining opposite ends of said cylindrical sidewall, said pair of material transfer ports is positioned in said end walls, said first plurality of material lifting members is mounted along a first portion of said cylindrical sidewall adjoining one of said end walls, said second plurality of smaller material lifting members is mounted along a second portion of said cylindrical sidewall adjoining the other of said end walls, and said plurality of individual burners is mounted along said second portion of said cylindrical sidewall and said other end wall.
 7. Apparatus as in claim 6 wherein said second portion of said cylindrical sidewall extends over about half the length of said drying drum.
 8. Apparatus as in claim 7 wherein said burners are inclined against the direction of rotation of said drying drum at an angle of about 45* with respect to a tangent to said cylindrical sidewall.
 9. Apparatus as in claim 8 wherein said burners have separate outlet cross-sections for a combustion gas and for air.
 10. Apparatus as in claim 9 wherein said material lifting members comprise material lifting boxes. 